In recent years, coating methods have been introduced into the production process of electronic devices such as electronic papers, flexible sensors, and RFID (Radio Frequency IDentification) tags. The use of coating methods enables to avoid vacuum processes and high temperature processes, and thus allows for a low cost production of electronic devices.
Among such electronic devices, RFID tags are expected to be used for all kinds of commodities, and the low cost production of RFID tags is highly demanded. Accordingly, techniques have been investigated to produce respective components included in an RFID tag using coating methods.
One of the components included in an RFID tag is a memory element, such as, for example, a ferroelectric memory element. In a ferroelectric memory element, the polarization generated by the application of an electric field to the element is maintained even when the electric field is reduced to 0. Further, by applying an electric field in the direction opposite to the direction of polarization, it is possible to invert the direction of polarization. This phenomenon is referred to as a polarization inversion, and the electric field intensity required for the polarization inversion to occur is referred to as a coercive electric field. A low coercive electric field allows a memory element to perform its functions, such as writing, storing, and reading of memory information, at a low voltage.
To produce a ferroelectric memory element using a coating method, a method is known in which a solution of a fluorine resin, such as a copolymer of polyvinylidene fluoride and polytrifluoroethylene (PVDF-TrFE), is coated, and the solvent therein is dried to form a ferroelectric layer (see, for example, Patent Documents 1 and 2).
Further, barium titanate, lead zirconate titanate and the like are known as inorganic ferroelectric materials. To produce a coating-type ferroelectric memory element using such materials, a technique is proposed, for example, in which a film formed by coating a varnish containing particles of these materials is used as a gate insulating film of a thin film transistor (TFT) (see, for example, Patent Document 3).